Accelerated tests for the prediction of cut-edge corrosion of coil-coated architectural cladding. Part I: Cyclic cabinet salt spray

摘要

Various accelerated cabinet tests have been used for the evaluation of the cut-edge corrosion of coil-coated architectural cladding. These include the conventional ASTM B-117 method (5% continuous NaCl spray), the standard Prohesion test (0.35% (NH_4)_2SO_4+0.05% NaCl wet/dry spray) as well as modified wet/dry spray tests using a relatively dilute artificial acid rain solution, shallow specimen incline angles with variations in the ratio of the wet and dry periods. Comparisons with outdoor exposure samples reveal that the B-117 test shows unrealistic corrosion morphology with the most realistic cut-edge corrosion given by the modified tests. Furthermore, with all types of wet/dry test specimen-to-specimen variation is considerably reduced compared with the continuous salt spray test. In the novel wet-dry tests the acceleration factor appears consistent with the number of wet and dry cycles however, the overall acceleration factor is limited and, hence, test times are extended. It is concluded that, over a 1000 h test time, the standard Prohesion test appears to show the best combination of realism and acceleration.